The 4000 series is a family of industry standard integrated circuits (IC) which implement a variety of logic functions using Complementary Metal–Oxide–Semiconductor (CMOS) technology, and are still in use today. They were introduced by RCA as CD4000 COS/MOS series in 1968, as a lower power and more versatile alternative to the 7400 series of TTL logic chips. Almost all IC manufacturers active during the era fabricated chips from this series. RCA sometimes advertised the line as COSMOS, standing for COmplementary Symmetry Metal-Oxide Semiconductor. The naming system followed the RCA convention of CA for analog, CD for digital, but did not relate to the Texas Instruments SN7400 series numbering scheme.
4000 series parts have the advantage of lower power consumption, wider range of supply voltages (3 V to 15 V), and simpler circuit design due to the vastly increased fanout. However their slower speed (initially about 1 MHz operation, compared with bipolar TTL's 10 MHz) limits their applications to static or slow speed designs. New fabrication technology has largely overcome the speed problems, while retaining backward compatibility with most circuit designs. Although all semiconductors can be damaged by electrostatic discharge, the high impedance of CMOS inputs makes them more susceptible than bipolar transistor-based, TTL, devices. Eventually, the advantages of CMOS (especially the later series such as 74HC) edged out the older TTL chips, but at the same time ever increasing LSI techniques edged out the modular chip approach to design. The 4000 series is still widely available, but perhaps less important than it was two decades ago.
The series was extended in the late 1970s and 1980s to include new types which implemented new functions, or were better versions of existing chips in the 4000 series. Most of these newer chips were given 45xx and 45xxx designations, but are usually still regarded by engineers as part of the 4000 series.
In the 1990s, some manufacturers (e.g. Texas Instruments) ported the 4000 series to their newer HCMOS technology with devices such as the 74HCT4060 providing equivalent functionality to a 4060 IC but with greater speed.
Design considerations 
The original 4000 series was available in either unbuffered or buffered inputs and outputs. The buffered outputs can source or sink more current than the unbuffered outputs, eliminating the need for discrete switching transistors in some designs. The buffered versions also have faster output switching times, as the signal rise time of the buffered output stage is faster than that of an unbuffered device. However the overall propagation delay through the buffered versions is higher due to the additional circuitry. The buffered devices are more susceptible to output oscillation with slow-changing inputs. Designers must evaluate the choice of buffered or unbuffered parts according to the nature of the circuit in which the devices are being used. The additional input and output gates on the buffered parts also make them marginally less susceptible to damage by electrostatic discharge (ESD).
Although the original designation for unbuffered and buffered parts was the addition of an 'A' or 'B' suffix to the part code (e.g.: 4000A = unbuffered, 4000B = buffered), some manufacturers (e.g.: Texas Instruments) later changed to using UB (unbuffered) and B (buffered) suffixes (e.g.: 4000UB and 4000B).
The diagrams below show the construction differences between a simple buffered and unbuffered CMOS NOR logic gate. Note that the logic gate at the core of the buffered part is actually a NAND gate, but the overall function of the complete circuit is a NOR gate due to the logic inversions performed by the buffers. (A negated NAND with negated inputs becomes a NOR as defined by De Morgan's laws in Boolean Algebra.) The clamping diodes on the inputs are to offer some protection against ESD.
The 4000 series permits the use of "cookbook" design, where standard circuit elements can be created, shared, and connected to other circuits with few, if any, connection difficulties. This greatly speeds the design of new hardware by reusing standard approaches to circuit design. In contrast, TTL circuits, while similarly modular, often require much more careful interfacing, since the limited fanout (and fan-in) require that the loading of each output be carefully considered. (Some later TTL families, like 74LS reduce this problem with fanouts of 20.) It is also much easier to prototype LSI designs using the 4000 series and get repeatable and transferable results when moving to the more integrated design.
Some care needs to be taken with the design of circuits using CMOS chips. Many parts offer multiple logic gates in a single package and it is common to not need all of them. An engineer who forgets to 'tie off' (connect the unused gate inputs to VSS or VDD) may find the chip draws excessive current. The problem is caused by biasing in each gate. With the inputs disconnected, the gates may be biased into a mode where the outputs are partially conducting; this leaves the output buffer drawing a great deal of current since it is not fully on or off, creating a low resistance current path between the power supply rails.
Example common 4000 series chips 
- 4000 - Dual 3-Input NOR Gate and Inverter
- 4001 - Quad 2-Input NOR Gate
- 4002 - Dual 4-Input NOR Gate OR Gate
- 4008 - 4-Bit Full Adder
- 4010 - hex non-inverting buffer
- 4011 - Quad 2-Input NAND Gate
- 4017 - Decade Counter / Johnson Counter
- 4511 - BCD to 7-segment LED driver
Notable parts 
A few parts are notable in the 4000 series because of their level of integration compared to other chips. This list is intentionally incomplete and is meant to provide a sample of the more interesting parts in the series. Devices useful for switching analog signals (such as the 4066, and 4051 to 4053) have continued to enjoy popularity in some audio designs (although non-4000 series chips, often with less distortion, are now available).
4017 decade counter 
|1||6||The 6th sequential output|
|2||2||The 2nd sequential output|
|3||1||The 1st sequential output|
|4||3||The 3rd sequential output|
|5||7||The 7th sequential output|
|6||8||The 8th sequential output|
|7||4||The 4th sequential output|
|8||0 V, VDD||The connection to the 0 V rail|
|9||9||The 9th sequential output|
|10||5||The 5th sequential output|
|11||10||The 10th sequential output|
|12||CO||Carry out output - outputs high on counts 0 to 4, outputs low on counts 5 to 9 (thus a transition from low to high occurs when counting from 9 back to 0)|
|13||LE||Latch enable - latches on the current output when high (i.e. the chip counts when LE is low)|
|15||RST||Reset - sets output 1 high and outputs 2 through 10 low, when taken high|
|16||+9 V, VCC||The connection to the +VCC rail (voltage between +3 V and +15 V)|
Example: Electronic Roulette 
4026 counter and display decoder 
The 4026 IC is a 16-pin CMOS seven-segment counter from the 4000 series. It counts clock pulses and returns the output in a form which can be displayed on a seven-segment display. This avoids using a binary-coded decimal to seven-segment decoder, but it can only be used to display the (decimal) digits 0-9.
|2||CI||Clock inhibit - when low, clock pulses increment the seven-segment|
|3||DE||Display enable - the chip outputs to the seven-segment when this is high (i.e. when it's low, the seven-segment is off) - useful to conserve battery life, for instance|
|4||DEO||Display enable out - for chaining 4026s|
|5||CO||Carry out output - Is high when changing from 9 to 0. It provides an output at 1/10 of the clock frequency, to drive the clock input of another 4026 to provide multi-digit counting.|
|6||F||Output for the seven-segment's F input|
|7||G||Output for the seven-segment's G input|
|8||VDD||The connection to the 0 V rail|
|9||D||Output for the seven-segment's D input|
|10||A||Output for the seven-segment's A input|
|11||E||Output for the seven-segment's E input|
|12||B||Output for the seven-segment's B input|
|13||C||Output for the seven-segment's C input|
|14||UCS||Ungated C-segment - an output for the seven-segment's C input which is not affected by the DE input. This output is high unless the count is 2, when it goes low.|
|15||RST||Reset - resets all outputs to low when taken high|
|16||VSS||The connection to the +9 V rail|
4511 BCD to seven-segment decoder 
|1||2s||Input for the 2s bit from the binary counter|
|2||4s||Input for the 4s bit from the binary counter|
|3||LT||Lamp test - when low, the chip takes all the segments on the display high (to test connections, etc.)|
|4||BI||Blanking input - when low, the chip does not output to the display - to conserve battery life, for instance|
|5||LE||Latch enable - latches on the current output when high (i.e. the inputs change the output when LE is low)|
|6||8s||Input for the 8s bit from the binary counter|
|7||1s||Input for the 1s bit from the binary counter|
|8||0 V, VDD||The connection to the 0 V rail|
|9||E||Output for the seven-segment's E input|
|10||D||Output for the seven-segment's D input|
|11||C||Output for the seven-segment's C input|
|12||B||Output for the seven-segment's B input|
|13||A||Output for the seven-segment's A input|
|14||G||Output for the seven-segment's G input|
|15||F||Output for the seven-segment's F input|
|16||+9 V, VCC||The connection to the +9 V rail|
See also 
- List of 4000 series integrated circuits
- 7400 series
- List of 7400 series integrated circuits
- Logic gate
- Wright, Maury. Milestones That Mattered: CMOS pioneer developed a precursor to the processor EDN, 6/22/2006
- "ATTITUDE CONTROL MAGNETOMETER"
- "AO-40 RUDAK Experiment Controller"
- Understanding Buffered and Unbuffered CD4xxxB Series Device Characteristics. Texas Instruments
- Lancaster, Don. CMOS Cookbook, ISBN 0-672-21398-2